1. Field of the Invention
The present invention relates to methods for preparing an epoxide, and more particular to, a method for preparing an epoxide by using a Ti—Si molecular sieve as a catalyst.
2. Description of the Prior Art
There are various methods for preparing epoxides such as chlorohydrination, co-oxidation, direct oxidation and etc. In the chlorohydrination for preparing epoxides, chlorine-containing waste water is formed and causes pollution to environment. In the co-oxidation for preparing epoxides, the process is complicated and various joint products are formed. The direct oxidation may be oxygen direct oxidation or peroxide direct oxidation. In the oxygen direct oxidation, pure oxygen is the reactant, and the process is simple and has no intermediate, but the selectivity of the product is low. Currently, the peroxide direct oxidation is widely used, wherein a Ti—Si molecular sieve is used as a catalyst, and the catalyst is easily separated from the product. The peroxide direct oxidation causes no damage to environment, needs less oxygen, but has low selectivity and low yield of the epoxide.
Generally, crystal Ti—Si molecular sieves are prepared by a hydrothermal method. U.S. Pat. Nos. 5,290,533, 5,888,471, 5,977,009, 6,042,807, 6,083,864, 6,329,537, 6,972,337 and 7,288,237 disclose the hydrothermal methods. In the hydrothermal method for preparing a Ti—Si molecular sieve, the presence of an alkali metal ion or an alkaline earth metal ion causes unexpected formation of crystals, and thus catalytic activity of the Ti—Si molecular sieve is decreased, such that these metal ions should be avoided in the reaction solution.
Hence, there is a need to develop a method for preparing an epoxide with high conversion rate of reactants, high selectivity of products and high yield.